1. Field of the Invention
This invention relates to an undercarriage for railway vehicles with at least four wheelsets, or pairs of wheels, and with at least two wheelsets respectively combined into a truck, and connected to a truck frame by means of coupling and guide elements. Such a truck frame can generally be oriented so that it can pivot in relation to a vehicle frame.
2. Background Information
Essentially two types of problems must generally be taken into consideration in designing undercarriages of this type. These problems are:
stable running on straight sections of track throughout the entire range of speeds, and PA1 low-wear running in curves. PA1 guarantees a radial adjustment capability for the wheelsets when the train is negotiating curves; PA1 reduces wear to a minimum and thus guarantees good transmission of traction force in curves; and PA1 does not adversely affect stability when the vehicle is running in straight sections.
Known are undercarriages which use a rigid longitudinal guidance of the wheelsets to prevent self-excited vibrations and to guarantee a secure transmission of propulsion and braking forces. On account of the large restoring forces which are applied by such longitudinal guidance to counter the rotation of the wheelsets, these wheelsets essentially cannot be completely radially controlled in curves. The remaining off-track running tends to induce a lateral force directed outward on the leading wheelset of the truck, and a force directed toward the center of the curve on the trailing wheelset. As a result of the momentum effect, the truck is controlled anti-radially. This is designated as "sideways running" or "rear free running". This behavior in curves results in large friction forces between wheel and rail, and in correspondingly high wear.
By selecting lower rigidities in the wheelset longitudinal guides, of course, the running behavior in curves can be improved, but such reduced rigidities also adversely affect stability when the vehicle is running on straight sections of track. The demand for low wear during negotiation of curves and sufficient stability when running on straight sections of track therefore generally requires a compromise with regard to the longitudinal restraint of the wheelset.
Also known are undercarriages which have two opposite wheelsets coupled to one another by means of a mechanical coupling device, and on which the wheel profile and longitudinal restraint of the wheelset is designed so that the elastic restoring forces which counteract the rotation of the wheelsets on the truck frame are less than the longitudinal forces generated by the conicity of the running surface of the wheels. Such cross-coupled running gear mechanisms have the disadvantage that, on account of the low longitudinal rigidity of the wheelset guides, additional connecting rods are required to transmit traction and braking forces. Special wheel profiles are also required.
Other designs have attempted to combine good running in curves and high stability by converting the rotational movement between the truck frame and the vehicle frame by means of levers into a radial adjustment of the wheelsets. Because the angle of rotation of the two trucks is generally different, the leading truck tends to be set for too large a radius of curvature, while the trailing truck tends to be oversteered. In addition to this disadvantage, an additional unfavorable characteristic of such designs is the complexity of the mechanical coupling elements, such as levers and joints, which can become lost, fall off, or become worn.
Improvements are possible with the use of elastomer elements as joints. But these joints tend to have greater elastic play, and therefore perform the transmission function only to a limited extent. The couplings between the vehicle frees and the wheelsets can also have a negative effect on stability when the vehicle is running on straight sections of track.